In a conventional cartridge mountable in a liquid ejecting device and supplying the liquid ejecting device with liquid, Japanese Patent Application Publication No. 2005-125738 discloses a liquid cartridge that can detect an amount of liquid left in the liquid cartridge. This patent document includes a detection member within the liquid cartridge. A float member is fixed to the detection member. The float member moves in response to the amount of liquid in the liquid cartridge and the detection member also moves along with the movement of the float member. The liquid cartridge according to patent reference 1 detects a position of the detection member with an optical sensor, thereby detecting the mount of liquid remaining in the liquid cartridge.
However, this patent document assumes that the position of the detection member detected by the optical sensor exists in the liquid. Therefore, if the liquid in the liquid cartridge has a tendency not to transmit light, such as black pigment ink, for example, accurate detection of the position of the detection member may sometimes become difficult.